A series of 37 aliphatic and aromatic sulfur-containing compounds were evaluated in 2-day Tetrahymena pyriformis population growth impairment assay. The results indicate that, except for select compounds, the in-ring sulfur-containing compounds, sulfates, sulfites, thiols, sulfones, and sulfoxides model as neutral and noncovalent-reacting narcotics. Abiotic loss due to volatility appears to interfere in accurate model prediction because actual toxicity was less than predicted. Vinyl sulfones and sulfoxides are more toxic than predicted using neutral narcosis. Tetrahymena exposed to methyl vinyl sulfone exhibits a direct relationship between the exposure concentration and the generation times with no lag phase in growth. As such, these population growth kinetics mimic those reported for hydrophilic neutral narcotics (i.e., ethanol and acetone). Tetrahymena exposed to phenyl vinyl sulfone exhibit a long concentration-dependent lag phase, which is followed by population growth at rates not different from controls. These population growth kinetics are similar but more dramatic than those reported for hydrophobic neutral narcotics (i.e., butylbenzene and 2-decanone). These results are useful in that they imply that sulfur-containing compounds for the most part act as simple narcotics. Therefore, their toxicity can be modeled with simple structure-toxicity relationships without much fear of underestimation of potency.
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